Rapid-crystallizing polyphenylene sulphide compositions

ABSTRACT

The invention relates to highly crystalline, rapid-crystallizing, thermoplastic compositions of polyphenylene sulphides and carboxylic acid esters.

The invention relates to highly crystalline, rapid-crystallizing,thermoplastic compositions of polyphenylene sulphides and carboxylicacid esters.

Polyphenylene sulphides can be used as raw materials for preparingfibres, sheets and shaped articles. Owing to their partly crystallinestructure, they have excellent properties, for example high wearresistance, favourable creep resistance properties and high dimensionalaccuracy. They are therefore highly suitable for the production ofmechanically and thermally highly stressed parts.

An additional improvement in the mechanical properties can be obtainedby incorporating reinforcing materials, for example glass fibres.

However, the production of shaped articles from polyphenylene sulphideby injection moulding is problematical since high mould temperatures(>130° C.) and relatively long moulding times are necessary. Mostinjection moulding processors cannot use mould temperatures of >130° C.and more since the moulds are normally designed for a temperature ofaround 100° C. (heating agent water). Mould installations which areoperated with other heating agents, for example oil, and attaintemperatures of >110° C. are generally rare, and their use posesproblems. Very frequently even they in practice do not attain thedesired temperatures, and the temperature distribution is uneven. Owingto these disadvantages, it can be economically unrecommendable to usesuch high mould temperatures in the injection moulding sector.

Furthermore, it is desirable to attain high crystallinity as rapidly aspossible in order to obtain optimum properties. High crystallinityensures hardness, dimensional stability, and shape stability, even atrelatively high temperatures. Also dependent on the mould residence timeis the length of the injection cycle with codetermines the economics.

These cycles are relatively long even at the high mould temperatures forthe processing of polyphenylene sulphide and hinder the advance ofpolyphenylene sulphide in the production of injection mouldings.

It has now been found that polyphenylene sulphides have highercrystallinity and crystallize more rapidly when they contain 0.5-30% byweight, relative to polyphenylene sulphide, of monomeric carboxylic acidesters. This allows the degree of crystallinity required for high shapestability to be reached more rapidly and the polyphenylene sulphidecompositions thus to be processed in much shorter injection cycles.

A further advantage of the polyphenylene sulphide compositions accordingto the invention consists in the reduction of the mould temperaturewithout the advantageous crystallization properties being unpaired. Theinjection moulding composition cools down more rapidly, thus furtherreducing the mould residence time.

The invention relates to highly crystalline, rapid-crystallizingthermoplastic compositions consisting of:

(a) 70-99.5, preferably 90-98.5, particularly preferably 93-97, % byweight of a polyphenylene sulphide having a melt viscosity of at least 5Pas, preferably of at least 50 Pas to 1200 Pas (measured at 306° C.under a shearing stress of 10³ Pa) and

(b) 0.5-30, preferably 1.5-10, particularly preferably 3-7, % by weight,relative to (a) and (b) of a monomeric carboxylic acid ester.

Representative compounds which are used as monomeric carboxylic acidesters (in the context of the specification and claims the term"carboxylic acid esters" is to be understood as including the carbonicacid esters of formula II) have the following formulae (I) or (II):##STR1## in which R₁ represents identical or different radicals of alinear or branched C₁ -C₂₅ -aliphatic, cycloaliphatic, C₁₀ -C₂₄-aromatic or C₇ -C₂₄ -araliphatic carboxylic acid,

R₂ represents identical or different radicals of a linear or branchedaliphatic, cycloaliphatic, araliphatic or aromatic alcohol having 1 to20, preferably 5 to 15, carbon atoms,

m represents the number 0, 1, 2, 3, or 4,

n represents the number 1 when m represents the number 0, and representsthe number 0 when m represents the number 1, 2, 3 or 4, and

y represents the number 1, 2 or 3.

R₁ and R₂ preferably represent C₁ -C₈ -alkyl radicals. They can havesubstituents which substantially do not react with the polyphenylenesulphide under injection moulding conditions, for example C₁ -C₄ -alkylgroups, NO₂ groups, etc.

Other examples of monomeric carboxylic acid esters are: dioctyl adipate,dinonyl phthalate, neopentylglycol dibenzoate.

The present invention further relates to a process for preparing highlycrystalline, rapid-crystallizing, thermoplastic compositions, which ischaracterized in that 70-99.5, preferably 90-98.5, particularlypreferably 93-97, % by weight of a polyphenylene sulphide having a meltviscosity of at least 5 Pas, preferably of at least 50 Pas to 1200 Pas(306° C., 10³ Pa) and 0.5 -30, preferably 1.5-10, particularlypreferably 3 to 7, % by weight of a monomeric carboxylic acid ester aremixed by adding the carboxylic acid ester to the polyphenylene sulphidemelt and homogenizing the mixture in the melt.

The invention furthermore related to a process for injection mouldingthese thermoplastic compositions obtainable according to the invention,which process is characterized in that a mixture of a polyphenylenesulphide having a melt viscosity of at least 5 Pas, preferably of atleast 50 Pas to 1200 Pas (measured at 306° C. under a shearing stress of10³ Pa) and a carboxylic acid ester are cast into moulds which have atemperature of no more than 120° C., the amount of carboxylic acid esterbeing chosen in such a way that the injection-moulded polyphenylenesulphide has at least 70% of the crystallinity which is obtained wheninjection moulding a moulding from unmodified polyphenylene sulphide atmould temperatures of at least 130° C.

Polyarylene sulphides can be prepared in a known manner fromdihalogenorarmatics and alkali metal sulphides in solution (for exampleU.S. Pat. No. 2,513,188).

The monomeric carboxylic acid esters can be prepared by esterifying orreacting carboxylic acids, their anhydrides, acid chlorides and/or thecorresponding dialkyl derivatives with aliphatic, cycloaliphatic,araliphatic or aromatic alcohols.

A detailed description of the different methods of preparation is givenfor example by H. Henecka et al in Houben-Weyl, vol VIII, page 359-680(1952); by E. Muller in Houben-Weyl (1963), 1 et seq.; Georg ThiemeVerlag, Stuttgart 1963; and in V. V. Korshak and S. V. Vinogradova,"Polyesters", Pergamon Press, Oxford 1965, pages 34-63.

Preferred monomeric carboxylic acid esters are those which are thosewhich are derived from carboxylic acids such as adipic acid, azelaicacid, sebacic acid, 2-ethylhexanoic acid, lauric acid, stearic acid,phthalic acid, trimellitic acid, benzoic acid and alcohols such asethylene glycol, propanediol, butanediol, hexanediol,di-/tri-/tetra-/oligoethylene glycols, neopentylglycol, pentaerythritol,2-ethylhexanol, octanol, nonylalcohol, decyl alcohol, butanol,octybenzyl alcohol, butylbenzyl alcohol and stearyl alcohol.

The preparation of the mixture of polyphenylene sulphides and carboxylicacid esters can be carried out on commercially customary mixingapparatuses. Suitable such apparatuses are kneaders and single-screw andtwin-screw extruders. For further processing, the mixture obtained canbe granulated after the melt has solidified.

The polyphenylene sulphide compositions can additionally contain fillersand/or reinforcing materials in the form of powders, fibres or mats.Examples thereof are metals such as steel, copper, aluminium or carbon.Preferred fillers are quartz, talcum or kaolin, preferred reinforcingmaterials are glass fibres. Preferred amounts of fillers, relative tothe total compound, are between 5 and 60% by volume.

The compositions can optionally further contain inorganic pigments, suchas, for example TiO₂, ZnS, phthalocyanines, carbon blacks, Cd pigments,spinels or organic dyestuffs, flow aids, mould release agents such as,for example, hydrocarbon waxes, ester waxes, amide waxes, UV-absorbersand/or stabilizers.

To further increase the flame resistance of the products, they canadditionally contain customary flame-retarding additives such as, forexample, those which contain halogen, phosphorus, phosphorus nitride,optionally in combination with oxides of the elements of subgroup V suchas, for example, antimony oxide.

The rate of crystallization of the polyphenylene sulphide compositionscan be further increased by adding inorganic or organic nucleatingagents. This is carried out as a matter of course with injectionmoulding compositions. The amounts are 0.05 to 5, preferably 0.1 to 1%by weight. The preferred nucleating agent is microtalcum.

The polyphenylene sulphide compositions according to the invention areexcellent starting materials for preparing sheets and fibres, preferablyfor preparing shaped articles of any kind by injection moulding.

EXAMPLES

The polyphenylene sulphide compositions according to the invention wereprepared by mixing and homogenizing the base components (see Table 1)with a 30 mm Werner and Pfleiderer twin-screw extruder at a melttemperature of 310° C. The extrudates, chopped into granules, were driedovernight.

The isothermal rate of crystallization of the dried granules wasmeasured by means of TLC apparatus. Pretreatment of the samples: heatedto 330° C., maintained at this temperature for 1 min and quenched inliquid nitrogen. The amorphous samples were allowed to crystallize outisothermally at 110° C. in the TLC apparatus, the change in the heat ofcrystallization being recorded as a function of time (exothermic peak).

As a measure of the rate of crystallization, the time required to reachthe maximum is recorded in Table 1 as a half-value time.

The samples 1-8 according to the invention listed in Table 1 consist ofa polyphenylene sulphide having a melt viscosity of 90 Pas (measured upto 306° C. and a shearing stress of 1000 Pa), 3.5% by weight of amonomeric carboxylic acid ester, 40% by weight of glass fibres and 5% byweight of microtalcum. Example 9 is a corresponding polyphenylenesulphide sample without carboxylic acid, for comparison.

                  TABLE 1                                                         ______________________________________                                        Exam-                Isothermal (110° C.) rate of                      ple   Carboxylic acid ester                                                                        crystallization half-value time [s]                      ______________________________________                                        1     Di-2-ethylhexyl                                                                              12                                                             adipate                                                                 2     Di-isononyl adipate                                                                          12                                                       3     Di-butyl adipate                                                                             12                                                       4     Benzyl butyl phthalate                                                                       24                                                       5     Di-octyl sebacate                                                                            26                                                       6     Di-Butyl laurate                                                                             26                                                       7     Tri-(n-octyl/n-decyl)                                                                        28                                                             trimellitate                                                            8     Tetra(pentaerythritol)                                                                       32                                                             stearate                                                                9     --             42                                                       ______________________________________                                    

We claim:
 1. A process for preparing an injection molded productprepared from highly crystalline, rapid-crystallizing, thermoplasticmixture consisting of(a) 70-99.5% by weight of a polyphenylene sulphidehaving a melt viscosity of at least 5 Pas (measured at 306° C. under ashearing stress of 10³ Pa) and (b) 0.5-30% by weight, relative to (a)and (b), of a monomeric carboxylic acid ester selected from ##STR2## and##STR3## where R₁ represents identical or different radicals of a linearor branched C₁ -C₂₅ -aliphatic, cycloaliphatic, C₁₀ -C₂₄ -aromatic or C₇-C₂₄ -araliphatic carboxylic acid, R₂ represents identical or differentradicals of a linear or branched aliphatic, cycloaliphatic, araliphaticor aromatic alcohol having 1 to 20 carbon atoms, m represents the number0, 1, 2, 3 or 4, n represents the number 1, when m represents the number0, and represents the number 0, when m represents the number 1, 2, 3 or4 and y represents the number 1, 2 or 3,by the process comprising firstmixing the carboxylic acid ester with the polyphenylene sulphide, whenthe polyphenylene is in a melt, and homogenizing the mixture in themelt, then casting the homogenized mixture into a mould which has atemperature of no more than 120° C., the amount of carboxylic acid esterbeing chosen in such a way that the injection-moulded polyphenylenesulphide has at least 70% of the crystallinity which is obtained ininjection moulding a moulding from unmodified polyphenylene sulphide atmould temperature of at least 130° C.
 2. A process in accordance withclaim 1, wherein R₁, R₂ or both have substituents which substantially donot react with the polyphenylene sulphide under injection moldingconditions.